Problem: Simplify the following expression: $n = \dfrac{1}{8r} - \dfrac{10}{3r}$
Explanation: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $8r$ and $3r$ $\lcm(8r, 3r) = 24r$ $ n = \dfrac{3}{3} \cdot \dfrac{1}{8r} - \dfrac{8}{8} \cdot \dfrac{10}{3r} $ $n = \dfrac{3}{24r} - \dfrac{80}{24r}$ $n = \dfrac{3 -80}{24r}$ $n = \dfrac{-77}{24r}$